Equations
by trillium33
Summary: Charlie struggles with his most unsolveable equation. Oneshot.


_A/N: This is based almost completely on actual episodes, especially "Uncertainty Principle" and contains many direct quotes, so if you consider that spoilers, then be warned._

_**Equations**_

_Something was different._

He had initially mistaken this particular pattern for a familiar one - all the elements had seemed to be there - but gradually subtle differences had made themselves evident, and he realized that his original conclusions were inaccurate.

He frowned, mentally applying the most obvious postulates, but he couldn't seem to make any of them fit. It was a complicated problem, one he had often wrestled with over the years, but never quite seemed to solve. Still, few problems were truly unsolvable. What he needed was more data.

Charlie's laptop was open across his knees, but the problem that held his attention wasn't on the screen. Instead, his gaze tipped over the top of the screen and fixed on the armchair a few feet away.

Don had arrived about a half hour ago, unannounced, per usual, had offered a cursory greeting and grabbed a beer from the fridge, also per usual, and had settled nearby in one of the armchairs and flicked on the television, ostensibly to watch a baseball game. The immediate data indicated a normal evening when Don was free to share dinner with them: Charlie busy preparing a lecture, Dad busy outside while the savory aroma of brisket began to fill the house, Don busy with the ballgame until the time came to set the table. There was usually a steady thrum of quiet, unspoken companionship underlying these moments that Charlie had come to relish. And that's what was missing. He narrowed his gaze intently, since Don seemed to be unaware of being observed.

What was odd - what was off about this whole equation - was that even though he could see Don sitting just a short ways away, he got the distinct impression that he was alone in the room.

Data. He needed more data.

"Who's winning?" he asked innocently.

Don's head swiveled in his direction, his beer suspended, forgotten, in mid-air, and he stared for a moment as if trying to remember who Charlie was and what the heck he could be talking about.

But he wasn't an FBI Special Agent for nothing, and he recovered quickly. "Huh? Oh - " Charlie could almost see him scrambling through his brain for information, his eyes drifting hopefully back to the television screen for help. "Uh - too close to call."

Charlie nodded wisely, as though accepting that as an answer, and dropped his eyes back to his laptop screen, suppressing the urge to whistle. Wow. Don had no idea what was going on in the game in front of him. The _baseball_ game in front of him. Just - wow. Something was definitely wrong.

He slumped down a little further behind the screen of his laptop, considering his research options. He could try asking Don what was wrong, but he knew how that would go - Don would tell him nothing was wrong. If he pressed that Don seemed upset, Don would assure him that he wasn't upset and if he pushed harder, would continue to insist that he was okay, that everything was okay. _Really. Really, Charlie. It's okay. Believe me. _No matter how exasperatingly obvious it was that just the opposite was so.

It was one of those things that he didn't understand about Don, had never been able to make sense of, no matter how hard he tried - the way that Don could insist on one set of conclusions, despite the hard core evidence to the contrary right in front of him. And Don was an FBI Agent - evidence should be his specialty, shouldn't it? Sometimes, it seemed to Charlie, it worked just the opposite way - that Don spent a lot of time ignoring the evidence - even denying it. Like that time he was shot.

Charlie remembered approaching the EMT truck in a daze, tiptoeing almost, as though treading too heavily would cause gunfire to erupt all over again. Don had glanced up, his face chalky and his eyes blank with shock. "Hey, Charlie," he had greeted him vaguely. "How ya doin'?"

_How am **I **doing? I'd say better than you, since I'm not the one bleeding! God, Don, sometimes you're so…_But his throat had closed spasmodically on an answer, heaving warningly, and he had had to swallow hard to force the rising bile back down.

Don had shaken off enough of the effects of shock to notice. "It's okay, really - " he had assured him firmly, tipping his head to indicate his injured arm. "It's fine."

Charlie had had a wild desire to laugh - to point out to Don that there was nothing, really, _nothing_ OKAY about getting shot - but at that point he'd realized that he was losing his battle to keep his stomach in place and had to clamp his teeth tight shut. Not that it had done any good. Two minutes later he was losing his lunch anyway. Just one more mess for the crime scene team to deal with. Humiliated and shaken, he had remained silent on the trip back to the Bureau.

Back there he had been determined to make up for his moment of weakness, but somehow the images had haunted him, stayed with him, distracting him. He had been _wrong. _Well, not wrong, really, just short of data, but that shortage of data had been fatal for three people - almost fatal for many more. Almost fatal for D - …but he couldn't think about that. Oh, who was he kidding. He couldn't think about anything else.

Still, he had tried to stick it out, to work on the new equations. Everyone else had seemed so calm - so matter-of-fact - even Don, wandering around with white gauze bundling his arm as if nothing special had happened. He'd decided that he would be matter-of-fact, too - overcome the embarrassing barfing incident - press on. But he couldn't. Everyone had assured him that it was perfectly normal, Don had insisted that he go home and get some rest.

Charlie had wanted to shake him. _Geez, Don, you were SHOT for God's sake - maybe you're the one who should be getting some rest? I mean, did it even occur to you to stop for five seconds and…? _But there had been no point in asking. He knew what the answer would be. Just like he knew what the answer would be right now. So instead, he had let a junior agent take him home, feeling deflated, feeling somehow that, for all he had grown and all he had done, he still couldn't keep up with the big boys. And feeling something else, too - something that he didn't quite recognize, couldn't quite name.

That was the feeling that had driven him to the garage, where he had intended to continue his work on the equations, and where instead, somehow, he had ended up in his sporadic battle with P vs. NP. It had been comforting; soothing.

Before he had started helping Don, his mathematics had always been safe and sane and wondrous and elegant - magical. Helping Don had exposed him to so many ugly, frightening, uncertain things, where the stakes were terrifyingly high and the consequences of an error dire. It was a new and different world for him, a world of shadows. He couldn't decide how he felt about it, so for a time he had lost himself in his old math world, where the stakes were strictly intellectual and the risks only of personal disappointment. Don, of course, had tried to shake him out of it. For a while he had half-hated him for it. And half-hated himself too, because he knew it was really no more than Don had to deal with every day.

He slid his eyes carefully over the top of the computer screen again. Unnecessary, really, since Don seemed to be equally oblivious to him and to the television in front of him, the neck of his beer bottle dangling unheeded from the fingers of one hand while the beer grew warm. No, this definitely wasn't satisfied, contented Don, relaxing after a successful case. He wanted to ask what had happened, what was wrong, what was bothering him, but what was the point? Charlie frowned. He would have to figure it out himself. All he needed was enough data and the right equation.

_Data. _Collecting data on Don had always been a challenge, though - Don didn't give it up easily, kept so much to himself. It only made Charlie rabidly curious, and he found himself doing what he always did when he needed data - digging around on his own. Of course, Don tended to see this more as invasion of his privacy and Charlie supposed, rather sheepishly, that he was right - he just couldn't seem to help himself. What a problem wouldn't willingly disclose, he felt compelled to root out. It got him into trouble sometimes. His father was always warning him, had warned him again when he found Don's missing box, but - well - it just seemed like he should _know_ that his only brother had been engaged. And if nobody would tell him…

Still. While he had felt a little hurt at first at the discovery, and left out, the sight of the returned engagement ring and "Dear John" letter had given him pause, and his face had suddenly flamed self-consciously. That _was_ private - and badly as he would like to know more, he knew that it was time to return Don's memories to him until he chose to share them freely. So, in the wee small hours of the morning, he had carefully packed all the items back in the box and called a cab.

On the way to Don's apartment, the hurt had faded some. In all fairness, he hadn't exactly made himself available for confidences. Probably it wasn't easy to tell the details of your crushed love life to the back of somebody's head while they frantically worked an unworkable equation. And there had been so much to do - to deal with - with Mom sick.

By the time he'd paid the cab driver and entered the lobby of Don's apartment building, he was just feeling sad. He'd never really thought about what Don might have given up to leave Albuquerque and return to LA. Now he wished he'd asked. Or at least shown an interest. Don had never been good at volunteering information about what he perceived as his disappointments or failures, but he might have responded to a little nudge. He peeked over the top of the screen again. He wondered how he'd respond to one now.

He rummaged around in his head for a conversation starter. He'd tried the baseball game. He looked at the laptop screen in front of him. Probably opening a discussion on Germain's Primes wasn't going to do it. He could always start telling Don about one of the top secret cases he had worked on for an agency other than the FBI. That ought to get a reaction.

Don had been horrified when he'd started to warn their dad about a possible biological threat in one of the early cases they'd worked together.

"It's against the law, Charlie!" he'd pointed out fiercely.

But - it's not like Dad was going to tell anyone, and his life - ?

"Charlie." Don had been firm, and Charlie was accustomed to responding to that tone in his voice. Later on, though, Don had asked him about his work with the NSA and Charlie had started to eagerly tell him.

Don had interrupted. "All right, no, stop, stop, stop - don't let me play you like that - you can't - . You can't tell me."

_Oh. _But Don was FBI, surely…?

Still, Don had asked him again, just a second later, and this time he had responded smartly, "Wouldn't you like to know?"

Don had started to smile, that slow, secret smile that crinkled the corners of his eyes, and Charlie knew that this time he had given the right answer. Don asked him again, and it had become almost a game between them, Don asking, Charlie refusing to tell, angling to provoke that smile. It always worked. He hadn't realized how ingrained Don's lessons in confidentiality had become until that time Larry started to disclose to Dad their calculations on the dirty bomb and HE was suddenly the one doing the shushing. When he'd told Don about it later, sure enough, there was the smile.

He was studying Don openly now, since he seemed to be oblivious, watched him knead unconsciously at his forehead, then his eyes. He'd sure give a lot to find a way to provoke that smile today.

Don had taught him a lot about keeping secrets, and he was grateful, but Don, he felt, on the other hand, kept too many and too well. When he had first found him at the EMT truck and was trying to spit out the questions that he couldn't seem to push past the hard lump in his throat, Don had finished reassuring him and then gone on to add, "Nothing to Dad, right? I'll take care of it." And when Charlie hadn't answered, "Charlie. Nothing to Dad. I'll take care of it, okay? You heard me, right?"

He had nodded, he guessed, but it had made him wonder. If he hadn't seen the shootout on television - shown up at the scene - would they have ever even known about the gunshot wound, or would Don have just appeared wearing long sleeves for a while? Did that mean that maybe there had been other gunshot wounds, other injuries that they knew nothing about? The thought made him mad, and if he hadn't been interrupted by vomiting, he might have actually confronted his brother about it. It wasn't as though he could use his usual method of data research to find out for sure, rummaging under Don's shirt for scars the way he rummaged through his stuff for clues, though the mental image of Don's probable reaction to that made him smile.

He sighed. He knew Don was just trying to protect them, but sometimes he took it too far. _You don't have to protect us from everything, Donnie. You're protecting us right out of your life. _

But habits were hard to break. Don had been protecting him for as long as he could remember - not just because he was older and bigger, but because, easily distracted by the magical formulas unfolding in his brain, Charlie had needed a little more protection than even the average kid brother. _You cross on the GREEN, Charlie, never the red, you understand me? See the green man walking? You wait for him. You never cross when you see the red man standing with his hands on his hips. Charlie? Are you listening to me, Charlie? Charlie, you heard me, right? _

Charlie had learned early that Don wouldn't let up until he was sure he had his attention - until he was sure that he had heard him. Sometimes Charlie wondered whether Don's tenacity was a natural part of his personality or just a necessary extension of having him as a younger brother. Whichever it was, it certainly hadn't lessened any over the years. So it hadn't really surprised him when Don had shown up to interrupt his frantic exploration of P vs. NP - to persuade him to get back to work on the equations he needed.

He had tried to explain - he really had - that he just couldn't do it any more - spilled out what was really worrying him - the devastating statistics on Don's chances of survival in similar circumstances. Don had brushed them aside like pesky, irritating flies, not worthy of consideration. _Buddy, it's not gonna happen! Look, understand, I appreciate you care about me…_

Jesus. _CARE about you? I don't CARE about you, Don, I LOVE you, you're my only brother, and if anything happened to you, I - I don't know…it's not that I don't know it's important - I DO know that - and the other people - they're the ones I CARE about… _

And that was the problem. That's why he was paralyzed on the horns of this dilemma. How was he supposed to decide? If he didn't help, innocent people could die. And if he tried to help the strangers, he risked his brother's life. How could he possibly make a choice like that? He couldn't choose - so he chose not to choose - or, rather, to choose P vs. NP. That was the kind of unsolvable problem that he knew how to handle.

How was it that Don chose, every day? He couldn't help wondering. How did he make it seem as though the answer was so easy, so obvious? What magical formula of his own did he use to calculate? A knotty problem in the equation. He couldn't work it out at all.

He had asked Don about it once - asked him how you lived with yourself if you were wrong. Don's answer had surprised him, even for Don - he had replied briskly that that couldn't happen - you couldn't _be_ wrong.

That was ridiculous, of course. Of course failure happened, statistically, it HAD to happen, and if there was one thing that Charlie understood, it was the odds. Given the length of Don's career, odds were it had already happened, many times. He sighed through his nose, eyes traveling from the beer bottle swinging, ignored, from the crook of Don's fingers, to Don's face, set and brooding. Odds were it was what had happened today.

Of course, Charlie hadn't gotten to continue his work on P vs. NP in peace, because of course Don had come back later to try again. Charlie hadn't been surprised, really: it wasn't the first time his immoveable object had run smack up against Don's irresistible force. Don had argued with him, Charlie hunching his shoulders away, as if not seeing Don would somehow make the words go away, too, as though not looking at the bulky bandage still branding his arm would banish memories of that wound as well.

_Charlie? Do you hear me, Charlie? Are you listening…?_

_Yeah, I hear you fine, Donnie. Sometimes I just don't like what you have to say. You could die, Donnie, and I just can't - I'm sorry. I can't. I'm not like you - I can't pretend that it will all work out right, just because I really want it to. I can't ignore the odds. What about those odds, Donnie? Were **you** listening? Did you hear ME?_

Finally, Don had thrown up his hands, the bandage blazing whitely against the dark of the trees, and turned away, his face tight with exhaustion and frustration. _I wish you'd snap out of your precious bubble for once._

And then he was gone. Charlie had stood there for a long time, that odd feeling that he couldn't name quivering in his stomach. He'd drifted inside and talked to his father, and that had helped some. After a while, he had wandered back to the garage and stared at the equations filling the blackboards along the walls and ceiling.

His precious bubble. It was precious. _It's nice in here, Don, you have no idea how nice. Nobody bleeds in here, nobody dies. Everything is solved eventually, if you work hard enough at it. It's logical. Clean. Exciting. Beautiful. You should try it, Donnie._

But Don couldn't join him in his bubble - he knew that. So if he stayed in there, then he was protecting himself right out of Don's life, too. Was that really what he wanted?

He had rolled a piece of chalk between his palms, following the path of the equations with his eyes. Larry had warned him about confusing being able to use math to predict with being able to use math to control. He had told Larry that he knew the difference. He had been lying, of course, though he probably hadn't fooled either of them. He liked the control. He liked that, eventually, he was almost bound to find an answer. Not like with Don. The Don-equation always left him feeling flummoxed and unbalanced.

Of course, Larry's words had proved prophetic. Seconds later he had spotted the shoot-out on television and realized how little control he really had; over anything that mattered, anyway. Don didn't either. He knew Don wasn't stupid - anything but. So why didn't he seem to know that?

It reminded him of something else that Larry had said to him - about forgetting that the human element was, ultimately, unpredictable, and didn't respond in a logical manner. He'd mulled that over. His mother had said something like that too once, one Passover when he was seven and had pointed out the ridiculousness of setting out a glass of wine for Elijah. Elijah was dead - had been for thousands of years, if he had ever really existed at all - did they really think he cared if they poured him a glass of wine or not?

His mother had sighed and smoothed the hair back from his forehead, then smiled at him…but the smile had seemed a little sad. "Not everything can be explained with logic, sweetie," she had said gently. "Some things we just have to take on faith."

That one had stumped him for a while. Of course everything could be explained - eventually. You just needed the right data, the right equation. Faith? That was a puzzler. How did you quantify faith?

_Faith. _He'd studied the logic of his equations. That human element was what made up most of Don's job - the uncontrollable, unpredictable, logic-defying, human race. If Don studied the odds, let them lead him, then would he be able to do that job at all? Or would he end up like Charlie was right now, devastated by them, paralyzed? Even if he knew the odds, could he afford to focus on them? So then what figures did factor into his choices? Maybe that thing their mother had called faith?

Don _did_ have faith, he realized: in his team, in himself, and - Charlie's heart squeezed into a knot that was both pain and pleasure - in his baby brother and his equations. Don looked at the odds, then put them aside and went forward despite them - believing that what he did needed to be done and that therefore he would do it and take his chances: defy the odds. It was his job - who he was, even. Somewhere along the line, Don had stopped being just Charlie's protector and had got busy trying to protect the whole world. Charlie couldn't think of a better guy for the job.

There was nothing he could do to change Don, then - to stop him from taking impossible chances. With or against the odds, with or without his help, Don was going to keep pushing forward, do what he felt had to do. About the only thing Charlie could do to help was maybe…create some equations that would help _improve_ the odds for him. And have a little faith.

All of a sudden he knew what that ache, that unfamiliar feeling he had been carrying around for days, was. Protectiveness. Somewhere along the way the roles had leveled off and balanced and now he felt for Don what Don had always felt for him - the need to keep him safe.

He studied the blackboards. Some good work here - inspired, even. Ground breaking. If he continued, he might have a breakthrough, make history, maybe win another award. But suddenly his Hobson's choice seemed more like a no-brainer. He reached for an eraser. He had more important unsolvable equations to pursue.

He had been a little nervous as he'd entered the Bureau to show Don his new work, afraid Don would be angry with him, or, worse, disappointed in him. But Don had just looked relieved and glad to see him, had dropped everything to listen to an explanation of what he'd discovered. Later, when the team was prepping for their ambush, Charlie had hovered nearby, unable to tear himself away. Finally, he couldn't wait any longer and had actually entered the truck where they were suiting up.

Don had been busy fitting his earpiece, but had glanced up in mild surprise as he approached, wearing what Charlie privately thought of as his "laser look" - that look where his face remained impassive but his eyes were busy taking in everything, weighing and measuring it and drawing conclusions. All he said was, "Hey," but Charlie knew what he really meant was, _What the heck are you doing here? Is everything okay?_

Charlie wished he knew. There was so much he wanted to say, and he just didn't know how to say it. To say, _be safe. Be smart. Save the world if you have to, but make sure you come home for dinner. I like having you drop by, Don - I want you to keep dropping by for the next fifty or sixty years - so don't disappoint me. Don't let me down. _Instead he had choked out something about Heisenberg's Uncertainty Principle.

Don had grinned at him. "Charlie, it's all right. Tell Heisenberg that we're all over this."

But the grin really told him that Don had heard exactly what Charlie hadn't been able to find the words to say; told him, _Don't worry about me, buddy - I'm indestructible_; told him that they had finally heard each other perfectly. Then Don had slapped him reassuringly on the arm and strolled out of the truck, as calmly as if he was going to his desk.

Charlie had watched him go until he couldn't see him any more. _You're not indestructible, Don, but maybe, just maybe, together we can improve your odds. If that's what I can do for you, then that's what I'll do. That, and keep the faith. _

So he'd done what he thought Don would want him to do - gone home, acted as if everything was normal - as if he'd done all he could, and the only thing left to do was wait. Which it was. He'd prepared some classes, made dinner, acted as if nothing special was going on. He thought he'd done it really well. So when Don had actually walked through the door, looking worn but content, he was completely unprepared for the rush of dampness that filled his eyes.

Don must have noticed something, because he had asked, with his gaze directly on Charlie, if Terry hadn't called them? Charlie had stuttered assurance that she had, babbling a little, then ducked into the kitchen to fetch dinner. He lost track of the number of times that he twisted back over his shoulder to double-check that Don was really there, alive and unhurt. _Sorry, Donnie - I guess this faith thing is going to take a little work. I still really like my tangibles._

_Tangibles. Hm. _Charlie narrowed his eyes over the top of the laptop again. Don wasn't even turned toward the television screen any more, but was gazing off at some spot on the far wall, as if he was watching something play out there over and over. Charlie decided that he had had enough.

"Hey, Donnie," he offered sweetly. "Know what I'm thinking?"

_Ha. That got his attention. _Charlie had known it would. "Donnie" was their father's nickname, really - both a nostalgic remnant of childhood and a not-so-subtle reminder that Don might be a big, bad FBI agent, but he was still his little boy. Charlie only reverted to it on occasion - in sudden bursts of affection, or when he was feeling particularly "little brother", in need of comfort or reassurance. He watched Don's head snap in his direction, the "laser look" focused to figure out exactly why he was using it now.

"What's that, buddy?"

Charlie pretended to keep his eyes on his computer, watching Don without seeming to. "I'm thinking that it's a good half hour 'til dinner's ready - plenty of time to kick your butt at one-on-one."

Don was the one off balance this time, his face scrunched with surprise. Then his eyes slowly crinkled at the corners.

Charlie ducked his head to hide a grin of triumph. _Oh, yeah. That was the smile._

"You do, huh?" Don put down his beer and scrubbed his hands together to rid them of the lingering dampness of the bottle's condensation. "You know what _I'm_ thinking? I'm thinking you're having a delusional moment."

Charlie shrugged, supremely innocent. "Only one way to find out, I guess."

"Right." Don was already on his feet, more energetic than Charlie had seen him since he'd walked in. "And just for that cocky remark, I'm not cutting you any slack." He reached the door, tugged it open.

Charlie smiled to himself, noting the sudden bounce in his step. A little vigorous exercise, a good meal, and who knows? Maybe Don would even feel like talking about it. Or maybe not, but either way, he was bound to feel better.

_See, I'm not a kid any more, Donnie. I can look after you, too. Okay, maybe I need some practice, but I can learn. I've always been a quick learner._

"You coming, or did you actually come to your senses?"

Charlie swallowed a chuckle as Don's yell floated back through the open door.

"I'm just saving my work!" he called back. "And giving you a chance to warm up - I figure you need all the help you can get!"

The only reply was the vigorous patter of the basketball on blacktop.

Charlie's grin widened at the loud twang of the ball rebounding off the backboard. At the very least, Don would be tired enough to sleep tonight. Maybe he'd be able toconvince him to spend the night. Dad's morning waffles could go a long way toward healing a man's soul.

"Hey, Charlie! You're the one who wanted to do this!"

"Yeah! Coming!" Charlie watched his screen go blank and then closed the lid to his laptop.

_Easy._

_All it really took was the right equation._

_The End (August 2005)_


End file.
